Hithereto, many efforts have been made to impart a sustained release property to various kinds of pesticidally active ingredients having solid form or liquid form. When largely classified, the prior art methods for preparing a pesticide having the sustained release property include (1) a method comprising encapsulating a pesticidal active ingredient in micro-capsules (see Japanese patent application first publication "Kokai" No. 58-144204 gazette and Japanese patent application first publication "Kokai" No. 59-20209 gazette); (2) a method comprising converting a pesticidally active ingredient into an inclusion compound with cyclodextrin (see Japanese patent application first publication "Kokai" No. 58-21602 gazette and Japanese patent application first publication "Kokai" No. 59-53401 gazette); (3) a method comprising granulating solid particles of a pesticidally active ingredient for use in a pesticide preparation such as granules and powders etc., alone or together with a filler etc., and coating the resultant particulate cores with wax or one of various resins (see Japanese patent application first publication "Kokai" No. 57-126402 gazette and Japanese patent application first publication "Kokai" No. 60-202801 gazette), and others. Hitherto, however, no attempt was made to achieve an improvement in the art by depositing and adhering fine particles of a hydrophobic substance onto the particle surfaces of a pesticidally active ingredient having a solid particulate form so as to cover the particle surfaces of the active ingredient with the fine particles of the hydrophobic substance, and thus controlling the dissolution and release of said pesticidally active ingredient.
When a pesticide preparation having a solid state in the form of granules and powders is brought into contact with water after the application of said pesticide preparation for use, in some cases the active ingredient present in said preparation can rapidly dissolve out and be released from the pesticide preparation so that the concentration of the active ingredient as released exceeds such a concentration just required for the active ingredient to display its biological effects. In these cases, the active ingredient can occasionally bring about kill of the leave of crop plants or a phytotoxicity such as suppression of the growth of crop plants; and the active ingredient once released can be degraded or disappear fastly in water or soil; and also it can disappear due to its degradation under the action of light, with consequences that the period of time of the lasting of the biological activities of the active ingredient can be shortened. For these reasons, these various troublesome problems can be solved if such a measure is provided to ensure that the pesticidally active ingredient continues to release gradually over a prolonged period of time from the pesticide preparation only in minimum amounts of the active ingredient just required to achieve the control of a pest. Further, when the sustained release property can be imparted to a pesticide, the necessity of repeated applications of such pesticide at several times can be eliminated, and the pesticide can be utilized highly economically with serving to prevent the enviromental pollution. However, any of the known pesticides having the sustained release property as mentioned above are advantageous in some aspects but disadvantageous in another aspects in solving the aforesaid various troublesome problems.
Thus, certain pesticidal compounds cannot be encapsulated into micro-capsules or cannot be converted into the inclusion compound with cyclodextrin according to the nature of the pesticidal compounds, and for these reasons there exist such pesticidal compounds which cannot be processed into a pesticide preparation having the sustained release property. Even if the prior art methods for producing the pesticide preparations having the sustained release property are applicable, there often occur some cases where a satisfactory sustained release property cannot be obtained; where the pest-controlling activities of the resulting pesticide preparation are not displayed fully; and/or where lasting and prolongation of the biological activities as well as the reduction in the phytotoxicity of the active compound which are aimed at for one of the purposes of the pesticide having the sustained release property are not attainable to a full extent. Besides, for the reasons why the technique for production of a pesticide having the sustained release property is complicate and troublesome and the raw materials used therefor are expensive; and for another reasons, there are still remaining many problems that are to be solved in the technical aspect or in the economic aspect. As described in the above, therefore, the prior art technique for the production of a pesticide having the sustained release property has not yet been developed to a full extent, and a development of a novel technique therefor is now desired.
In account of the above situations, we, the present inventors, have paid attention on a technique of modifying or improving the structure of the surfaces of particles of such a pesticidally active ingredient having solid particulate form, and we have made researches in attempts to provide a novel agent which is able to give the desired sustained release property to a pesticide of the solid particulate form, and to provide such a pesticide having the sustained release property as obtained using said agent, and also to provide a process for the production of such sustained-releasing pesticide.